A method of regulating the preemphasis of channels from a Wavelength Division Multiplex (WDM) signal is known from WO 0209299 A2, in which a measurement of the optical signal-to-noise ratio OSNR is performed in relation to the amplified spontaneous emission ASE. Two variants for measuring the amplified spontaneous emission ASE between channels after admission by a periodic filter (interleaver filter) are described in which an extrapolation of the measured values of noise power between two channels or at the edge of the overall channel spectrum occurs. The point at which the noise power is measured, where the amplified spontaneous emission ASE occurs in different ways, is, however, system-dependent; i.e., it changes in accordance with the filter used through which the WDM signal passes. There is, therefore, no system-related adaptation for determining the noise power here. The measurement method also requires a great deal of effort since it is based on a measurement in a notch between two channels. As such, measurements must be taken before each interleaver filter and, at the link end, the entire measured values of the amplified spontaneous emission ASE must be added together. In practice, this means that a relatively expensive measurement unit must be connected before each filter.
An object of the present invention is, therefore, to specify a method which, depending on the filters or components used which influence the spectrum of the transmitted signals, allows the optical signal-to-noise ratios to be measured with; little effort.